U.S. Pat. No. 8,791,508 (incorporated by reference) describes electronic components such as diodes and transistors where the main current flows laterally through a thin gallium-aluminum nitride layer, AlGaN, formed on a GaN layer.
FIG. 1A is a cross-section view of a portion of a GaN Schottky diode which corresponds to FIG. 7 of U.S. Pat. No. 8,791,508. A non-doped silicon support 1 is covered with an aluminum nitride layer 3, with a non-doped GaN layer 5, and with a non-doped AlGaN layer 7. Palladium metallizations 9 are deposited on layer 7 and are surrounded with metallizations 11 of titanium-aluminum Ti—Al formed through layer 7. Metallizations 9 form Schottky contacts with the AlGaN and metallizations 11 are in ohmic contact by their sides with the AlGaN layer. Gold metallizations 15 are deposited on metallizations 9 and gold metallizations 17 are deposited on metallizations 11. The assembly is covered with an insulating layer 19.
AlGaN layer 7 bonded to GaN layer 5 is capable of conducting a current laterally between Schottky and ohmic metallizations 9 and 11. When the diode is forward biased, a current laterally flows from the sides of metallizations 11 towards the periphery of metallizations 9.
FIG. 1B is an example of a top view according to cross-section B-B of FIG. 1A. Metallizations 9 and 11 comprise an assembly of alternated parallel strips. Strips 9 form the teeth of a first comb, and strips 11 form the teeth of a second comb interleaved with the first one. Only three teeth are shown in FIG. 1A, a larger number of teeth being shown in FIG. 1B for a better understanding. Each of the combs is connected to a terminal, 20, 21, of the diode.
A problem is that if the teeth of the combs are long and narrow, a non-negligible resistance appears in the conductive state.